## Example

Problem: A grit channel has a volume of 1240 ft3. What is the detention time in minutes when the flow rate is 4.1 MGD?

Solution:

^ , „ 1240 ft3 x 7.48 gal/ft3 x 1440 min/day 0 „„ .

4,100,000 gal/day

Note: The tank volume and the flow rate must be in the same dimensions before calculating the hydraulic detention time.

### 6.5 CHAPTER REVIEW QUESTIONS

6.1 The influent flow rate to a primary settling tank is 1.35 MGD. The tank is 70 ft in length and 16 ft wide and has a water depth of 10 ft. What is the detention time of the tank in hours?

Use the following data for the remaining chapter review questions:

### Plant influent

Flow = 8.40 MGD Grit chamber Number = 2 Channel length = 60 ft Channel width = 4 ft Water depth = 2.8 ft Primary settling Number = 2 Length = 160 ft Width = 110 ft Water depth = 12 ft Anaerobic digester Flow = 19,000 gpd Volume = 110,000 ft3

6.2 What is the hydraulic detention time in hours for primary settling when both tanks are in service?

6.3 What is the hydraulic detention time in the grit channel in minutes when both channels are in service?

6.4 What is the hydraulic detention time of the anaerobic digester in days?

CHAPTER

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